This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Procumbent herbs or undershrubs. Leaflets 4 or 5. Flowers umbellate on axillary peduncles. Calyx-lobes often longer than the tube. Keel beaked. Upper stamens free. Pod oblong or linear, terete, turgid or flat. Of the fifty or more species there are only a few worthy of cultivation.
1. L. comiculatus. Bird's-foot Trefoil. - Some of the varieties of this very common native plant are very pretty for covering rock-work, etc, especially the double-flowered variety. L. Jacobaeus is the dark-purple-flowered species, formerly more cultivated than at present. It is a native of the Cape de Verde Islands, and therefore too tender to withstand our winters; but it may be treated as an annual. L. Gebelia, a taller growing species, growing in dense tufts, with glabrous and glaucescent foliage and rosy-carmine flowers. Native of Syria. L. purpureus and siliquosus (Tetragonolobus) are remarkable for their ample foliage, purple and yellow flowers, and 4 winged pods.